1. Field of the Invention
This invention relates to scanning and illuminating systems and methods for automated optical inspection. More particularly, to systems and methods to illuminate and inspect the inner bore of a stent or other tubular or conical device having an interior bore, where the interior bore may be either a through hole or a blind bore.
2. Description of Related Art
Stents are small wire mesh tubes used to hold open compromised arteries and other fluid conduits within a human body. The critical use of these devices and their small size requires stents to be manufactured to the highest possible quality standards.
Balloon expandable stents are vulnerable to failure during deployment. A sharp edge may puncture the balloon under high pressure causing a deployment failure. Also, arteries and vessels in the body flex and bend and a deployed stent must conform. Manufacturing defects may cause a point of weakness in the stent that is vulnerable to fatigue and failure as this point of weakness is repetitively bent or flexed in the vessel. Still further, if a portion of the stent breaks off and travels through the bloodstream, the patient is a risk of a stroke if this broken piece travels to the brain and lodges in an artery.
In view of the potential for catastrophic failure, rigorous inspection of the stent is required prior to deployment. Within the industry, visual inspection of stents has historically been done by human operators utilizing a microscope at 40× to 80× magnification. The stents are typically placed between two rollers and rotated under the microscopes while the human operator observes. An automated inspection system for measuring the dimensions of a stent and inspecting exterior surfaces is disclosed in U.S. Pat. No. 6,606,403, “Repetitive Inspection System with Intelligent Tools,” that is incorporated by reference in its entirety herein.
Summarizing the current state of the art and its deficiencies, to achieve an automated method for inspection, a complete image of the stent needs to be quickly taken in good focus with clear contrast. The current state of the art is to use a stereomicroscope such as the Olympus SZ40 and ringlight. The stent is placed between two rollers and manually rotated. Illumination is provided from above with a fiber optic ringlight. While a video camera can be used with such a microscope, as the stent rotates between the rollers it does not always turn smoothly so it can move in and out of focus. Human operators often readjust the focus knob of the microscope to accommodate this, but this would be difficult and time consuming for an automatic method. As such, systems and methods need to be developed to rotate the stent in a well-defined and fixed geometry so as to always keep the stent in focus.
Further video cameras that can be used in conjunction with microscopes generally can only bring a very small section of the stent in focus at one time. To image every section of the stent with such an approach would require a very large number of individual images. This would be impractically time consuming to generate. Thus a method is required to generate a complete image of the inside diameter of the stent in just a few seconds. The current state of the art also uses a ringlight that illuminates the top outer diameter of the stent as well as the inner diameter thus creating a confusing image with excess glare.
There remains a need for an automated system and method to illuminate and image the inner bore of a stent and thereby facilitate the inspection of that inner bore.